Jan, they do make a device that either reduces or advances the revs of
the speedo, and is adjustable. Many hot rods also have odd combinations
of tires, trans, rear ends, and this allows for the adjustment. With
the toploader and T-5, you just go to your Ford dealer, and ask for a
different gear for the end of the speedo cable. They are usually
identified by color, as in I want a blue one.
Larry
jeyerman@ix.netcom.com wrote:
>
> It would seem to me that this a very big market for an electronic
>speedometer- a small magnet glued to the driveshaft and a pickup somewhere
>near it-then an electronic speedo inside a Smith's case. An adjustment
>somewhere for rear axle ratio. To bad I don't know how to do this!
>
> Jan
>
> Jay_Laifman@countrywide.com wrote:
> > >Jay, after you give them the info from the speedo, what
> >do they do, and is the speedo accurate over the entire
> >range, and is so to what plus or minus mph?
>
> I just spoke to Mo-Ma. She told me that if she used to 1040 gauge I have
> (from a SIV Automatic), she could use a 41 tooth gear and get pretty close,
> but not exact. I may have to go to an external converter to get closer to
> exact.
>
> The speedo is a completely different issue. It is not fixed by gears. I
> know I am going to get corrected on this one. But, this is as close as I
> know - and as always, I'm willing to be corrected. Attached to the head of
> the cable is a flat disk with a magnet. This disc fits in a flat metal
> dish to which the needle is attached. There is nothing connecting the dish
> to the disk. When the magnet on the cable spins, it creates a magnetic
> force that lifts/turns the dish and the needle. As the dish spins faster,
> the force increases and turns the disc further. In order to calibrate the
> speedo then, they don't change gears, but change the amount of magnetism in
> the dish or the plate or both. There is also, I think, and adjustment to
> the resistance against the plate.
>
> That being said, I believe there is an inherent inaccuracy in the speedo
> needle such that it cannot be 100% accurate at all speeds. You need to
> pick what range you want to be most accurate, and live with the other
> zones. My driving takes me through a very long 45 mph speed trap. But,
> then 65 is always a concern. I don't know how wide the band is of
> accuracy. I'll probably shoot for right in the middle of those two.
>
> Jay
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